In general, a light emitting keypad is applied to communication equipment such as a mobile phone so that the light emitting keypad is used as a switch device for generating a signal or performing various additional functions. The light emitting keypad has the function of enabling identification of numeral or character keys in the nighttime or at a dark place. Recently, an ultra-thin light emitting keypad has been developed and employed as mobile phones become thinner.
FIG. 1 is a sectional view of a conventional direct illumination type LED (Light Emitting Diode) keypad that comprises a printed circuit board (100), domes (102), direct illuminating LEDs (103), and a keypad portion (104). The printed circuit board (100) has contact terminals (101). Here, the plurality of domes and direct illuminating LEDs are installed on a front surface of the printed circuit board. The keypad potion that has numerals or characters printed on an upper surface thereof and protrusions (105) formed on a lower surface thereof is installed in front of the domes and the direct illuminating LEDs.
In this direct illumination type LED keypad, the keypad portion is illuminated by light emitted from the direct illuminating LEDs installed on the front surface of the printed circuit board. That is, when a user presses a key of the keypad portion, a protrusion corresponding to the key of the keypad portion allows a corresponding dome to be connected to a corresponding contact terminal of the printed circuit board to generate a predetermined electrical signal. The generated electrical signal causes a corresponding LED to emit light so that the keypad portion can be directly illuminated by the LED in the form of a point light source.
However, the aforementioned direct illumination type LED keypad is manufactured to be relatively thicker since it is impossible to fabricate a thin keypad due to characteristics of the LEDs. Furthermore, the direct illumination type LED keypad may reduce a use time of a battery since power consumption increases according to light emission of the LEDs. Furthermore, there is difficulty in designing the direct illumination type LED keypad since light emission uniformity may be irregular in accordance with the arrangement positions of the LEDs.
FIG. 2 is a sectional view of a conventional EL (Electroluminescence) type light emitting keypad for solving the aforementioned problems. The EL type light emitting keypad comprises key tops (110), an EL metal dome sheet (120) and a printed circuit board (130). The EL metal dome sheet (120) comprises an EL sheet (121), metal domes (123) and a base tape (122), thereby achieving ultra-slimness and low power consumption.
As for the function of this EL type metal dome keypad, when a user presses the key top (110), a protrusion (111) disposed on a back surface of the key top (110) causes the metal dome (123) to be brought into contact with a fixed contact terminal (131) of the printed circuit board (130) so that the keypad is switched on and operated.
However, in the conventional EL type light emitting keypad, there is a high risk that the EL sheet may be damaged or broken since the EL sheet (121) is consecutively pressed and impacted by the protrusion (111), and thus, a severe problem of degradation of the reliability of EL is caused and there is also a problem in that a click feeling of the keypad is deteriorated. Furthermore, the conventional EL type light emitting keypad has problems in that the EL sheet has a life span shorter than that of an LED due to characteristics of the EL sheet, noise is produced in an LCD module, and reliability is lowered. Moreover, the conventional EL type light emitting keypad has a problem in that production costs increase as compared with manufacture of an LED keypad.